Hackage :: [Package]

speculation: A framework for safe, programmable, speculative parallelism

[ bsd3, concurrency, library ] [ Propose Tags ] [ Report a vulnerability ]

A framework for safe, programmable, speculative parallelism, loosely based on http://research.microsoft.com/pubs/118795/pldi026-vaswani.pdf

This package provides speculative function application and speculative folds. And speculative STM actions take the place of the transactional rollback machinery from the paper.

For example:

spec g f a evaluates f g while forcing a, if g == a then f g is returned, otherwise f a is evaluated and returned. Furthermore, if the argument has already been evaluated, we skip the f g computation entirely. If a good guess at the value of a is available, this is one way to induce parallelism in an otherwise sequential task. However, if the guess isn't available more cheaply than the actual answer, then this saves no work and if the guess is wrong, you risk evaluating the function twice.

The best-case timeline looks like:

[---- f g ----]
   [----- a -----]
[-- spec g f a --]

The worst-case timeline looks like:

[---- f g ----]
   [----- a -----]
                 [---- f a ----]
[------- spec g f a -----------]

Compare these to the timeline of f $! a:

[---- a -----]
             [---- f a ----]

specSTM provides a similar time table for STM actions, but also rolls back side-effects.

Changes in 0.3.0:

  • Speculative folds moved to Data.Foldable.Speculation and expanded to cover all of the Data.Foldable combinators.

  • specBy and specOn variants added.

[Skip to Readme]

Modules

[Index]

Downloads

Maintainer's Corner

Package maintainers

For package maintainers and hackage trustees

Candidates

  • No Candidates
Versions [RSS] 0.0.0, 0.0.1, 0.0.2, 0.1.0, 0.2.0, 0.3.0, 0.4.0, 0.5.0, 0.5.1, 0.6.0, 0.7.0, 0.8.0, 0.8.0.1, 0.8.0.2, 0.8.1.0, 0.8.2.0, 0.9.0.0, 1.0.0.0, 1.1.0.0, 1.2.0.0, 1.2.0.1, 1.2.0.2, 1.3, 1.4, 1.4.1, 1.4.1.1, 1.4.1.2, 1.5, 1.5.0.1, 1.5.0.2, 1.5.0.3
Dependencies base (>=4 && <6), parallel (>=2.2 && <2.3), stm (>=2.1 && <2.2) [details]
Tested with ghc ==6.12.1
License BSD-3-Clause
Copyright (c) 2010 Edward A. Kmett
Author Edward A. Kmett
Maintainer Edward A. Kmett <ekmett@gmail.com>
Category Concurrency
Home page http://github.com/ekmett/speculation
Uploaded by EdwardKmett at 2010-06-27T22:18:00Z
Distributions
Reverse Dependencies 3 direct, 8125 indirect [details]
Downloads 24746 total (2 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by Bayesian average]
Your Rating
  • λ
  • λ
  • λ
Status Docs uploaded by user
Build status unknown [no reports yet]

Readme for speculation-0.4.0

[back to package description]

speculation

This package provides speculative evaluation primitives for Haskell, very loosely based on the paper "Safe Programmable Speculative Parallelism" by Prabhu, Ramalingam, and Vaswani.

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.19.4622

Combinators

speculative function application

Various speculative function application combinators are provided. Two fairly canonical samples are described here.

spec

spec :: Eq a => a -> (a -> b) -> a -> b

spec g f a evaluates f g while forcing a, if g == a then f g is returned. Otherwise f a is evaluated.

Furthermore, if the argument has already been evaluated, we avoid sparking the parallel computation at all.

If g is a good guess at the value of a, this is one way to induce parallelism in an otherwise sequential task.

However, if g isn't available more cheaply than a, then this saves no work, and if g is wrong, you risk evaluating the function twice. spec a f a = f $! a

The best-case timeline looks like: [---- f g ----] [----- a -----] [-- spec g f a --]

The worst-case timeline looks like: [---- f g ----] [----- a -----] [---- f a ----] [------- spec g f a -----------]

Compare these to the timeline of @f $! a@: [---- a -----] [---- f a ----]

specSTM

specSTM provides a similar compressed timeline for speculated STM actions, but also rolls back side-effects.

speculative folds

A speculative version of Data.Foldable is provided as Data.Foldable.Speculation.

Each combinator therein takes an extra argument that is used to speculate on the value of the list.

foldr

foldr :: (Foldable f, Eq b) => (Int -> b) -> (a -> b -> b) -> b -> f a -> b

Given a valid estimator g, 'foldr g f z xs yields the same answer as Foldable.foldr' f z xs.

g n should supply an estimate of the value returned from folding over the /last/ n elements of the container.

As with spec, if the guess g n is accurate a reasonable percentage of the time and faster to compute than the fold, then this can provide increased opportunities for parallelism.

foldl

foldl :: (Foldable f, Eq b) => (Int -> b) -> (b -> a -> b) -> b -> f a -> b

foldl works similarly to Foldable.foldl', except that g n should provide an estimate for the /first/ n elements.

contact information

I can be reached through the user ekmett on github, as edwardk on irc.freenode.net #haskell channel, or by email to ekmett@gmail.com.

-Edward Kmett